Such a method can be used for important applications, especially for carrying out circular permutations of binary elements of a coding key to be used within a microcircuit card. The handbook entitled: "Les cartes a microcircuit" de F. Guez et al, edited in France by Manon, gives full explanation for this kind of coding. In the handbook "Security for computer networks" by D. W. Davies and W. L. Price, edited by John Willey and Sons, also more precise information is found about the algorithms used in these microcircuit cards.
With these kinds of cards, the problem is encountered of lack of space offered by the microcircuit. The space for storage of the programming information remains limited; it is therefore important that the various subprograms or routines forming part of this information have a minimum size and are used as frequently as possible.
This problem is more serious when the coding key formed by two half keys of 28 binary elements each must be processed, while the message to be enciphered or deciphered are separated into two blocks of 32 binary elements each. Therefore, there is a disparity between the format of these blocks of 32 binary elements and that of the half keys of 28 binary elements, which can be represented in the format of 32 binary elements. This format of 32 binary elements is considered as a global format, which is constituted by elementary formats of, for example, 8 binary elements each. In this case, an operation of rotation, to which these half keys are subjected within the global format, can lead to waste of programming information.